With the vic-ii removed...does the floppy work?

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finepie
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Re: With the vic-ii removed...does the floppy work?

Post by finepie »

All are in the 4 kohms range or higher, so I guess that means no shorts.
I've re-visited U27, which has a couple pins readings quite off. And its symptoms match according to carlsen's guide. I've ordered a replacement, fingers crossed... hope I don't just make things worse, I haven't soldered anything in a long time!


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Gyro Gearloose
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Re: With the vic-ii removed...does the floppy work?

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Yeah that makes sense, it generates some critical timing signals. If the readings are off, that's a candidate.
I really think the bigger chips are OK. And there is life, so this kind of fault is very plausible.
I hope you ordered several other ICs as well, since typically in these small quantities it's the shipping that's expensive compared to the parts.
Are you ordering from an electronics supplier or gambling with eBay parts?
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Re: With the vic-ii removed...does the floppy work?

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Well I feel a bit dumb, of course I should've ordered a pile of ICs since they're like 10 cents and the shipping is $5 :cry: well, next time...
I ordered from retroleum, they've been good before.
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Re: With the vic-ii removed...does the floppy work?

Post by Gyro Gearloose »

In the meantime you can watch soldering videos.
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Re: With the vic-ii removed...does the floppy work?

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Well, U27 has been replaced and..... nothing has changed! On the bright side that means I didn't break anything further in the process.

And, at least I leveled up my soldering and I can cross one chip off the suspect list, but, well, that was basically the only one actually exhibiting weird readings (still is, so really literally nothing has changed). I guess I'll sleep on it and see what I target next.
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Re: With the vic-ii removed...does the floppy work?

Post by Gyro Gearloose »

There are resistors here and there pulling signals up, do a visual check of resistors and physical wiggle (with power off) and see if there isn't a resistor somehow cracked or with a broken pin.
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Re: With the vic-ii removed...does the floppy work?

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Definitely nothing I can detect visually or with a wiggle. I'll need to disconnect the resistors to check them, so I guess I'll just have to do that.

Summarizing the main clues to help me get my thoughts straight:
- Ruled out: CIAs, SID, PLA, U27, kernal
- IRQ is low. That's on VIC 8, CPU 3, CIA U1 21, cart 4, RP4, and R51. Removal of vic, cpu, or cia makes it high.
- U26 has a few off readings on pins leading to ROMs, RAM and VIC
- user port B, keyboard pins 13-19, U28 6 and U28 12, are all high, these all go to CIA u1, but we know CIA isn't the culprit.

At this point I think, after a resistor check, I'll just blindly start replacing chips: VIC, U26, U28, U13, U25, U14... I guess in that order.
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Re: With the vic-ii removed...does the floppy work?

Post by Gyro Gearloose »

Well it's certainly going to have to work eventually... You're very patient. I'd replace cheaper stuff first.
I have sit down with a schematic and think things through.
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Re: With the vic-ii removed...does the floppy work?

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I've checked all the resistors (only a few needed to be disconnected in the end) and all are exactly as they should be.
I guess I'll order up those ICs...
I'm not sure if it's patience or obsession :lol: .... but at least I'm learning something along the way!
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Re: With the vic-ii removed...does the floppy work?

Post by Gyro Gearloose »

Well, you get me stumped, and I want to find the issue as well.
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